The essential ability to control locomotion with respect to the environment is based on the visual perception of optic flow patterns produced at a moving point of observation. Although a number of mathematical analyses of optic flow have been performed, little empirical research exists on the ability of observers to detect and utilize this information. The proposed project will examine age differences in the detection of optic flow information, as they pertain to the control of walking and driving. The specific aims of the study are to determine the abilities of young and old observers to detect properties of optic flow patterns that are specific to the following aspects of self-motion: (a) the direction or heading of rectilinear motion; (b) the path of motion during curve-taking; (c) the approach to and size of contours, brinks, obstacles, and apertures on the ground surface; (d) variables of the ground surface, such as texture and other markings, that influence the detectibility of these properties; and (e) observer variables such as size of the visual field, fixation, and visibility of the focus of expansion, that may affect performance. Optic flow displays will be generated by computer animation techniques, stored on video disk, and presented to subjects for judgment on a large rear-projection screen. The variables of optic flow rate, angle of path to the surface, and response task will also be manipulated. A basic understanding of how the visual control of locomotion changes with age has immediate applications to the clinical assessment of perceptual abilities on complex everyday tasks, the development of optical aids and retaining of perceptual skills to improve performance, and enhancing the visual structure of roadways and other environments to further the mobility of the elderly.